The migration crisis enveloping Europe and much of the Middle East today is one of the worst humanitarian disasters since the 1940s. Millions of desperate people are on the march: Sunni refugees driven out by the barbarity of the Assad regime in Syria, Christians and Yazidis fleeing the pornographic violence of Islamic State, millions more of all faiths and no faith fleeing poverty and oppression without end. Parents are entrusting their lives and the lives of their young children to rickety boats and unscrupulous criminal syndicates along the Mediterranean coast, professionals and business people are giving up their livelihoods and investments, farmers are abandoning their land, and from North Africa to Syria, the sick and the old are on the road, carrying a few treasured belongings on a new trail of tears.

It is the first migration crisis of the 21st century, but it is unlikely to be the last. The rise of identity politics across the Middle East and much of sub-Saharan Africa is setting off waves of violence like those that tore apart the Balkans and the Ottoman Empire in the 19th and 20th centuries. The hatreds and rivalries driving endangered communities to exile and destruction have a long history. They probably have a long future as well.

What we are witnessing today is a crisis of two civilizations: The Middle East and Europe are both facing deep cultural and political problems that they cannot solve. The intersection of their failures and shortcomings has made this crisis much more destructive and dangerous than it needed to be—and carries with it the risk of more instability and more war in a widening spiral.